1. Field of the Invention
The invention is directed to a graphic data processor for processing observed graphic data (hereafter graphic data signals). In particular, it is directed to a technique for the quantitative detection of the composition and grains in observed graphic data.
2. Description of the Prior Art
In the past, Fourier conversion has been generally applied in frequency analysis. For example, distribution of the frequency components may be determined by the following equation: ##EQU1## where one-dimensional signal x(n), (n=0.apprxeq.N-1), is obtained by AD conversion at a sampling frequency of Fs(Hz) over a period of T sec, where T=N/Fs, and j=the imaginary number.
In this method, however, signals are processed as a whole, and what is determined is the sum of the frequencies over the entire signal range. To obtain partial frequency distribution in this method, a signal has to be divided into a number of ranges, external Fourier conversion applied to each of these ranges, and a frequency distribution obtained for each. It is, however, not possible to calculate in this method the frequency every sampling period Ts(ACC)=1/Fs (momentary frequency of the signals) because of the following relation between the span Ta of the ranges and frequency resolution Fr. EQU Fr=1/Ta . . . (2)
The two-dimensional Fourier conversion shown in equation (3) is applied also to analyze spatial frequencies of images: ##EQU2##
However, this method of analysis also applies to images as a whole so that the spatial frequency distribution obtained here is the sum of the frequencies for the entire image. Thus, to apply the method to an image in order to determine the local spatial frequency distribution in it, the image must be divided into a number of small areas, two-dimensional Fourier conversion applied to each to these areas, and a spatial frequency distribution for the areas obtained. As in the case of one-dimensional signals, the more an area is reduced in size, the more does the frequency resolution deteriorate making it impossible to determine local spatial frequency for each picture element.